The subject matter of the present invention relates to a pump apparatus applicable to temporary completion of a well, such as the completion used when testing a well; and more particularly, to a new pump apparatus for pumping well fluids from a wellbore when a pressure of a formation traversed by the wellbore is not high enough to produce the well fluids at a satisfactory rate.
Oil wellbores traverse earth formations. For some wells, the formation pressure is not high enough to produce the well fluids to the well surface at useful rates. As a result, numerous pumping methods are known by those persons skilled in the art, which methods are associated with temporary completion of production wells, such as the completion used when testing a well.
One such pump apparatus is known as the Jet pump. The jet pump has a satisfactory output; however, the effluent that is produced is mixed with a lifting fluid and separation requires additional steps. In addition, the pump has a restricted flow path that can conflict with other phases of the operation. Furthermore, the jet pump requires communication (via the use of ports) between the production string and the annulus around the string in order for the pump to operate. Provision must be made to open and close these ports in order to enable other operations, such as stimulation and tubing conveyed perforation.
Another such pump apparatus is known as the Moineau pump. The Moineau pump generates lower flow rates than the Jet pump.
Furthermore, since it does not provide flow through capability when not activated, the Moineau pump does not allow for the implementation of other possible drill stem test activities.
Still another such pump apparatus, known as the Reda pump, is used primarily in completed wells, and is cumbersome when used in exploratory wells. In addition, it requires the use of electrical generating facilities where an electric cable must be disposed in the wellbore. It is more complex, and restricts the flow path.
Still another pump apparatus, known as the rotary inflate pump, is used to inflate a packer by pumping annulus fluid from a well annulus into a deflated packer via the pump apparatus. The rotary inflate pump operates by circumferentially rotating a top sub; a cam reciprocates in response to the rotation of the top sub; a single longitudinally disposed roller set (a pair of rollers disposed in the same cross-section) connected to the top sub is disposed in one serpentine shaped slot, which slot surrounds the periphery of the cam; as the top sub rotates, the single roller set rides in the single-slot of the cam thereby reciprocating the cam; the cam is connected to a piston; and a pair of check valves are fixedly connected to a housing of the pump, one check valve being an intake check valve communicating with the annulus, the other check valve being an exhaust check valve communicating with the deflated packer; as the cam reciprocates, the piston reciprocates thereby receiving the annulus fluid in the intake check valve during one stroke of the reciprocating piston and exhausting the received annulus fluid to the deflated packer during another stroke of the reciprocating piston. However, since only one serpentine shaped slot or groove is disposed around the periphery of the cam, the single roller set of the top sub disposed in the single slot of the cam limits the output pressure and the flow rate of the annulus fluid being pumped into the deflated packer. In addition, the rotary inflate pump did not pump fluid to the surface of a wellbore, rather, it pumped well fluid from an annulus disposed downhole to a packer also disposed downhole.
Consequently, another pump of different design is needed which overcomes the problems associated with the other above mentioned pumps and which pumps well fluids from wellbores, having low formation pressure, to the wellbore surface.